The adhesion of transformed cells is defective when compared with their normal counterparts, a property which potentially plays an important role in metastasis. The basis for this defect is being sought in terms of changes in the cell-to-substrate contacts developed by tansformed cells. The contacts are evaluated by interference reflection microscopy with emphasis on the stronger focal contact. The relative roles of different cell surface glycoconjugates in forming substratecontacts has been evaluated through reconstitution and inhibitor experiments on an adhesiondefective mutant and its wild-type. Collectively, the experiments show a specific requirement for glycosylated cell surface proteins, as opposed to gangliosides or proteoglycans, in the ability to form the focal contact. A functional role for substrate-adsorbed fibronectin, as opposed to other spreading factors such as platelet factor 4, has been demonstrated in the formation of the focal contact. Experiments are in progress to isolate cell surface proteins involved in substrate adhesion. Development of the cytoplasmic precursor of the focal contact will be studied at the ultrastructural (HVEM) and immunochemical levels in normal cells. Defects in the various steps in forming the cytoplasmic precursor, and in the required cell surface glycoconjugates, will be sought in order to explain changes in the substrate contacts and hence adhesion of transformed cells. The significance of low levels of fibronectin on transformed cells will be evaluated in terms of its role in the formation of the two substrate contacts. Spontaneously, chemically and virally transformed cells will be examined.